If you just want backup, but intend to leave accessible, my suggestion would be: - if accounts are IMAP, check 'account settings' >'syncronization&storage and verify that the folders are ticked for download/offline and also sync all messages. - Then, if accounts are IMAP click File>offline>download to ensure all messages are downloaded - next, click help>troubleshootinginformation, - scroll down to 'profile folder' and click 'open profile - exit thunderbird - for IMAP accounts , click Imapmail folder and copy each account folder to external media - Repeat the process at Mail folder for each POP account - Now, for any that you do not want to leave accessible, start TB and remove those accounts.